Pipes that contain and transport water are used in numerous applications, which are generally divided into the broad categories of non-pressure and pressure applications. The present invention is useful on pipes suitable for both non-pressure and pressure applications and is particularly useful in sewage and drain pipes. Other applications for the present invention are also contemplated, such as conduit sections used for housing telecommunications cable, fiber optics cable and electrical wire or cable.
Pipe can be installed in a number of ways, one of which is the traditional pipe laying technique of simply digging a trench and then placing the pipe sections in the trench, assembling the sections into a pipeline and then covering the pipeline. There are also trenchless pipe installation methods known as microtunneling, sliplining and pipe bursting, which are described below. The present invention can be used in traditional applications and is particularly useful in trenchless applications.
Microtunneling describes a process in which a vertical access shaft is excavated to the pipe's starting grade. The term starting grade means the level, or depth, at which the pipe will be installed. A second vertical access shaft is constructed at the ending location for the pipeline, the pipeline therefore being erected between the two vertical shafts. A microtunneling machine, which is usually a remotely controlled, steerable, boring machine having a cutter head at one end, is lowered into the first access shaft. The microtunneling machine bores or cuts through the wall of the shaft and the cutter head drills a tunnel through the soil towards the second access shaft. The soil that is displaced by the cutter head is removed by either an auger system, by which the soil is mechanically moved from the hole, or a slurry system, which uses water to flush the loose soil from the hole.
Before the entire microtunneling machine exits the access shaft and enters the tunnel, a pipe section is attached to the rear of the machine. Axial compressive force, or pressure, directed along the longitudinal axis of the pipe section, is applied to the end of the pipe section opposite the machine. This force pushes the machine forward, with the pipe section attached, into the tunnel towards the second shaft. A second pipe section is then attached to the first, then a third is attached to the second and so on. This process of adding additional pipe and pushing the machine forward continues until the machine enters the second access shaft. At that point, an entire length of pipe, consisting of a plurality of pipe sections, is formed between the access shaft and the second shaft. The machine is then disconnected from the pipe and the pipeline is complete.
During the tunneling process, the machine is advanced forward by pushing against the end of the last pipe section attached and transmitting axial compressive force through the connected pipe sections. Therefore, the pipe sections must be joined in a manner so that a significant amount of axial compressive force can be transmitted through the joints without buckling, or otherwise damaging the joints or the pipe sections. Furthermore, the tunnel formed by the microtunneling machine is preferably just slightly larger than the diameter of the pipe because the larger the diameter of the tunnel, the greater the chance that the tunnel will collapse. If the pipe joints include sections that project outward from the diameter of the pipe wall, a larger tunnel must be bored to accommodate the pipe joints and there is a greater chance that the tunnel will collapse. Therefore, it is important that the pipeline have a smooth outer surface.
Sliplining is a method of rehabilitating deteriorated pipelines by inserting a new, small diameter pipe, called a slipliner pipe, inside of an existing large-diameter pipe. When sliplining, an access pit is dug to an existing pipeline; the access pit being slightly longer than the length of one section of the slipliner pipe. The top half of the section of existing pipe exposed at the bottom of the access pit is removed leaving the bottom half which is known as a pipe cradle. A slipliner pipe section is then placed inside the pipe cradle and is pushed into the existing pipe, parallel to the longitudinal axis of the existing pipe. A second slipliner pipe section is then lowered into the pipe cradle and joined to the first section. The second pipe section is then pushed into the existing pipe causing the first pipe section to advance further into the existing pipeline. Additional pieces of pipe are joined and the assembled pipe is advanced until the existing pipeline is completely sliplined or until the next access pit is reached. When the sliplining is completed, grout or other sealing material is pumped into the gap between the existing pipe and the new pipe along the entire length of existing pipe that was sliplined.
Often, the existing pipe to be sliplined is broken and dilapidated. The existing pipe's joints are sometimes separated and pieces of debris or sections of the existing pipe extend into the pipe cavity creating obstructions. Furthermore, if slipliner pipeline has flared, or wide, joints, the pipeline inserted into the existing pipe will have a relatively small diameter as compared to the existing pipe and therefore may not be capable of transporting a large enough volume of liquid. Therefore, it is important that a slipliner pipe have a smooth outer surface. Additionally, slipliner pipe sections also must be capable of efficiently transferring an axial compressive force from one pipe section to another.
Pipe bursting is another method of pipeline rehabilitation in which the existing pipe is replaced by a pipe having a diameter equal to or larger than the existing pipe. In this method, access is first gained to an existing pipe through a manhole or access pit. A small diameter steel pipe is inserted through the existing pipeline to a second access location. A pipe bursting head, which is generally a solid metal cone, is then attached to the steel pipe at the second access pit. The steel pipe with the pipe bursting head attached is then retracted towards the first access location by pulling the pipe. As the bursting head is pulled through the existing pipe, the existing pipe bursts into pieces that are displaced into the soil. A new pipe is pulled behind the pipe bursting head and creates a new pipeline. Pipe bursting creates numerous snags or obstructions, which are usually pieces of broken existing pipe. Therefore, it is important that the outer surface of the new pipe be smooth and have no projections.
When forming a length of pipe to be used in the above-described applications, several pipe sections are generally mated, or joined, in an end-to-end relationship and the connection between the mated, or joined, pipe sections is referred to as a joint. Many types of pipe joints are disclosed in the prior art.
U.S. Pat. No. 2,032,492 to Nathan discloses a pipe joint assembly particularly useful for terracota and ceramic pipes, wherein the pipe is molded and includes a first end having a larger diameter than the second end. When two pipes are joined, an annular flexible gasket is placed on the smaller diameter end of the first pipe and this end, including the gasket, is inserted into the large diameter end of the second pipe thereby forming a waterproof joint.
U.S. Pat. No. 4,565,381 to Joelson discloses a concrete pipe wherein one end of the concrete pipe has a tongue element extending about the annular periphery thereof and a flexible, stepped sealing element is attached to the tongue. The second end of the pipe has a groove element having a stepped sealing surface. The stepped sealing surface of a first pipe section is joined with the tongue on a second pipe section, whereby it seals against the stepped flexible seal.
U.S. Pat. No. 3,998,478 to Zopfi discloses a sealing joint construction, including a gasket, specifically for use with plastic pipes. The joint is formed by inserting a spigot (i.e., a narrow) end of a first pipe section into a bell (i.e., a flared) end of a second pipe section. Preferably, the bell end is "double belled" meaning that it has a narrow diameter bell section and a wider diameter bell section. The spigot end of one pipe section is received in the narrower bell portion of a second pipe section and part of the barrel, i.e., the main body of the pipe, of the first pipe section adjacent the spigot end is received in the wider bell portion of the second pipe section. The outer end of the second pipe section, which is formed adjacent the wider bell portion, is wider than the barrel of the first pipe. Hence, an annular groove is defined between the inner wall of the outer end of the second pipe section and the outer wall of the barrel and a flexible gasket is disposed in the groove to form a water-tight seal.
U.S. Pat. No. 4,796,669 to St. Onge discloses a method for relining pipeline with interconnectable plastic pipe sections. The plastic pipe sections are joined by either: 1) threading the end of one pipe into the end of another pipe, 2) using a buttress-type thread to interlock one end of one pipe to the opposite end of the second pipe, 3) forming two opposed, angular members, respectively, on either end of the pipe, the mating ends of two pipe sections sliding together and snap-fitting into position, or 4) joining the pipe sections by means of lap-joint members formed within the pipe walls and then preferably taping the outer periphery of the joint.
The prior-art structures encounter problems when used with a pipe having a variable wall thickness, especially if the pipe is used in microtunneling, slipjoining or pipe bursting applications. First, as previously described, it is advantageous to form a pipe consisting of pipe sections wherein the pipe has a smooth outer surface. This requirement eliminates the use of external collar joints and most bell and spigot joints, which usually have a section protruding from the outer surface of the pipe. Furthermore, even joints formed within the walls of the mated pipe sections, such as lap joints, do not provide a smooth outer surface if formed in a variable thickness wall.
Second, the pipe sections must be joined so that a significant amount of axial compressive force can be applied to the end of one pipe section and be transmitted through the joints to the other pipe sections in such a manner that the joints do not flex, buckle or telescope; the term telescoping meaning that the end of one pipe section is forced inside of the body of another pipe to which it is joined. This requirement eliminates the use of most joints formed within the walls of mated pipe sections because the application of a significant axial compressive force will cause the joints to deform or separate. Even when a standard lap joint is used, if the pipe sections have a variable wall thickness, the mating surfaces of the lap joints do not align properly because of the variation in wall thickness. This can cause one wall to bear the entire load which may cause the wall to deform and the joint to fail.
Finally, a constant-width gap between the lap joint members of the first pipe section and second pipe section must be maintained so that a gasket may be inserted to form a water-tight seal. Until this time, when joint profiles were formed in pipe sections having variable width walls, the profile dimensions varied as the thickness of the wall varied. Therefore, the profile formed in one pipe section rarely, if ever, properly aligned and mated with the profile formed in another pipe section. If a gap was created by the joining of two pipe sections, its dimensions varied according to the variations in the respective wall thicknesses of the pipe sections that were joined. As it will be understood, if the gap into which the gasket, or sealing member, is retained is too wide, the gasket will not form an adequate seal. If the gap is too narrow, the fit is too snug and the pipe sections cannot be joined.